The present invention relates to film of thermoplastic elastomer type, permeable to water vapor and to many gases.
In all the that followed, the term "film" is used according to the definition of it given in the Modern Plastics Encyclopedia; i.e., a planar section whose thickness is very low in comparison to its length and width.
It is considered that the thickness of a film is generally below 250.mu.m.
In European Patent published under No. 46,071 there is the description of a water vapor permeable film consisting of a mixture of polyurethane and of a polymer incompatible with the polyurethane, such as polystyrene.
In European Patent Published under No. 141,592 a water vapor permeable film is proposed, consisting of a mixture of incompatible polymers based on ethylene/vinyl acetate copolymer and on vinyl polymer.
In European Patent published under No. 52,915 there is a description of a polyurethane film which is nonporous and permeable to gases.
Now, the permeability of these films to gases and in particular to water vapor is not very satisfactory, this being especially so in the case of films of low, or even of very low thickness.